Polyamide (Nylon) Sutures

How nylon is made

Polyamide is a macromolecule whose repeating units are joined by amide bonds — the same linkage, chemically, that joins one amino acid to the next in a protein. Suture-grade nylon is commonly Nylon 6, and the route to it is ring-opening polymerisation: caprolactam, a cyclic amide, has its ring broken under heat in an inert atmosphere, and the opened units link into long chains. The molten polymer is then extruded through a spinneret to draw it into filaments.

The name carries the chemistry. Caprolactam’s ring contains six carbon atoms, so the polymer made from it is Nylon 6. Other nylons — polymerised from different monomers, or from monomer pairs — are numbered on the same principle, and the numbers are counting carbons rather than grading anything.

The interesting part: non-absorbable, but not unchanging

Here is the nuance that makes polyamide worth reading carefully. An amide bond is hydrolysable — water can cleave it. That is not a marginal claim about nylon; it is the same reason the peptide bonds in a protein can be broken down. And in tissue, over long periods, nylon’s amide bonds do slowly hydrolyse. The material is not chemically frozen in place.

Yet polyamide is classed non-absorbable, and correctly so. The classification asks whether the body breaks the material down and metabolises it as part of its normal chemistry — the way it handles an absorbable suture, on a timescale measured against wound healing. Nylon is not handled that way. The slow hydrolysis of its amide bonds is a fact of the polymer’s chemistry operating over a quite different timescale, and it does not make the material absorbable in the sense the category means.

The lesson generalises across this cluster. “Non-absorbable” is a statement about metabolism, not a promise of permanence. Silk is the other member of the class that makes the same point from a different direction. Polypropylene, whose backbone is a pure hydrocarbon chain with no hydrolysable bond in it at all, is the contrast case. All three sit in the same category, and their chemistry is not the same — which is exactly why the category is a starting point for reasoning rather than the end of it, and why what a given product does over time is stated in its instructions for use rather than inferred from its class.

Construction and colour

Polyamide suture is commonly extruded as a monofilament: one continuous filament, no interstices between filaments, and so no capillarity. Braided polyamide exists too, and the trade-offs there are the ones braid construction always brings — pliability and knot seating on one side, interstices and surface texture on the other.

As a monofilament, nylon carries memory: it holds the shape of the pack and has to be worked out of it. It is commonly supplied dyed black, which is an identification and visibility aid and has no bearing on how the material behaves. Colour and gauge availability are product-specific; the product page lists what is offered.